At present, in the aspect of speed regulation of large rotation machineries, the permanent magnet speed regulating devices (sometimes referred to as the permanent magnet coupler or permanent magnet eddy current speed governor or the like) have gain recognition and favorable comments. These devices have the following major characteristics: (1) The torque is transmitted via an air gap, and no mechanical contact is needed. (2) Stepless speed regulation may be achieved. (3) Light-load soft startup is implemented, and the impacts caused by the motor to the power grid are reduced. (4) The load vibration is isolated, and the damages caused by the load to the device are mitigated. (5) The over-load protection function is implemented. (6) Safety and reliability are ensured, and the repair rate and maintenance cost of the device are reduced. (7) No electromagnetic wave interference is caused. A representative of such devices is the product manufactured by Magna Force, Inc., in the United States (U.S. Pat. No. 5,477,094). The permanent speed regulating device disclosed in this patent works based on the following principles: the conductor rotor disc and the permanent magnet rotor disc move relatively to each other, the conductor rotor disc rotatably cuts the magnetic lines in the alternating magnetic field generated by the permanent magnet rotor disc to generate an induction eddy current, the induction eddy current generates a reverse inductive magnetic field, and the inductive magnetic field interacts with the magnetic field of the permanent magnet disc, such that an electromagnetic torque is generated between the conductor rotor disc and the permanent magnet rotor disc. The electromagnetic torque is reduced by regulating the size of the air gap between the two rotor discs or regulating the coupling area between the two rotor discs with respect to a cylinder structure.
In addition, China Patent Application CN101931309A discloses a highly-efficient permanent magnet coupling device for transmission shaft, comprising at least one armature winding rotor disc and a mated armature winding disc shaft coupling mechanism, at least one permanent magnet rotor disc and a mated permanent magnet disc coupling mechanism, and corresponding input and output shaft couplers; wherein the armature winding rotor disc comprises at least one group of armature windings and an armature winding installing disc for mounting the armature windings, and the armature windings are nested or mounted in an armature slot arranged on one side of the armature winding installing disc; the permanent magnet rotor disc comprises a group of at least two permanent magnets and a permanent magnet installing disc for mounting the permanent magnets, and the permanent magnets are respectively N and S polar-alternately and uniformly nested or mounted on the circumference of the permanent magnet installing disc; the side of the armature winding rotor disc provided with the armature windings face towards the side of the permanent magnet rotor disc provided with the permanent magnets, to form electromagnetic coupling installation centering the center line of the same axis; an air-gap spacing is defined between the armature winding rotor disc and the permanent magnet rotor disc, and the armature winding rotor disc is linked to the corresponding input shaft coupler or output shaft coupler via the mated armature winding disc shaft coupling mechanism, and the permanent magnet rotor disc is linked to the corresponding output shaft coupler or input shaft coupler via the mated permanent magnet disc shaft coupling mechanism. This patent further discloses five specific solutions of the armature winding structure (for example, see claim 3). Overview of all these five solutions finds that “the head end and the tail end are short-circuited” inside the rotor disc to form a “closed-loop short-circuit coil”. The working principles are the same as the product manufactured by Magna Force, Inc. The difference lies in that the eddy current in the conductor rotor disc is “combined” to the interior of the armature winding coil. The air-gap spacing between the armature winding rotor disc and the permanent magnet rotor disc determines the electromagnetic torque that may be transmitted therebetween. That is, the techniques disclosed in the prior art all teach regulating the torque by regulating the air gap between two rotors. Since the output torque is in a positive proportion to the load, coupling of the transmission shafts or regulating the transmission torque and driving the load is achieved. Therefore, the air gap between the rotor discs in each permanent magnet coupling assembly is regulated, and thus the load rotation speed is regulated.
As well known, in the permanent magnet speed regulation techniques, a rotation speed difference needs to be present between the permanent magnet rotor and the conductor rotor; otherwise, no electromagnetic torque is generated between two rotor discs. That is, the input rotation speed n1 is constantly greater than the output rotation speed n, and then the rotation speed difference s is equal to (n1−n)/n1. This formula is transformed into n=n1(1−s). It is apparent that the input rotation speed n1 may not be changed with respect to the permanent magnet speed regulating device. As seen from the above formula, if the output rotation speed n is to be changed, that is, the speed regulating function needs to be implemented, the rotation speed difference s needs to be changed. In other words, the rotation speed regulation by the permanent magnet speed regulating device is essentially rotation speed regulation, i.e., slip speed regulation. The speed regulation is based on the principles of changing s by changing the output torque, wherein when the output torque is smaller than the load torque, the rotation speed is lowered, and on the contrary, the rotation speed is increased. In the prior art, two approaches are available for changing the output torque. One is to change the magnetic flux area between the permanent magnet rotor and the conductor rotor. The other is to change the air gap between the permanent magnet rotor and the conductor rotor. However, these two approaches both need a mechanical execution mechanism. However, configuration of the mechanical execution mechanism not only makes the structure of the transmission device more complicated, but also increases the volume and improves the subsequent maintenance workload.
In addition, in the prior art, such a rotation speed regulating device is subject to a great slip power loss. If the mechanical loss and stray loss are ignored, the slip power and the output power satisfy the following formula: Pm=sPm+(1−s)Pm. In the formula, Pm denotes the input power, sPm denotes the slip power, and (1−s)Pm denotes the output power. As seen from the above formula, when the input power Pm is not changed, a greater s indicates a greater slip power sPm and a smaller output power (1−s)Pm. In the permanent magnet speed regulating device in the prior art, the slip power sPm is dissipated as heat energy on the device. Therefore, when the regulated speed of the permanent magnet speed regulating device is greater, more heat is generated. For example, when s=0.5 (that is, speed regulation by 50%), if the mechanical loss and stray loss are ignored, the transmission efficiency of the permanent magnet speed regulating device is only 50%. Therefore, such permanent magnet speed regulating device is defective in the working principles in terms of low transmission efficiency and great energy loss.